Charge pump regulator with load current control

ABSTRACT

A multiple output regulating charge pump includes a load current regulator to balance currents in multiple branches of at least one load, such as light emitting diodes in a parallel configuration. The load current regulator includes current mirror circuits to provide substantially identical currents to the respective light emitting diodes, thereby producing uniform light from each of the light emitting diodes. The multiple output charge pump includes a charge storage component that is alternately charged during a charge cycle and discharged during a discharge cycle. The charge pump provides current to a second load during the charge cycle and to a first load during a discharge cycle.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/211,167, filed on Jun. 13, 2000, and entitled A Single Mode,Buck/Boost, Regulating Charge Pump, A Method to Improve the EfficiencyThereof, and a System Using the Charge Pump in a Combination LED CurrentRegulator and Voltage Converter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of voltage converters and inparticular to a charge pump voltage converter.

2. Description of the Related Art

Many electrical devices require power supplied at a stable voltagedifferent than that provided by a primary power source. In manyapplications, the primary power source is a battery. Often theelectronic devices require voltages that are between 1 and 2 times thevoltage provided by the battery. An additional requirement is that thevoltage provided be relatively stable. A low voltage can result in thepowered devices failing to operate at all or at a reduced performancelevel. Steady overvoltage can reduce the life of the devices orpermanently damage the devices. Spikes or transients in voltage can alsodisrupt device operation and cause damage.

One difficulty with batteries is that many batteries do not provide astable output voltage. The output voltages of many batteries decrease asthe batteries are used and as the batteries age. The voltages can alsovary depending on how heavily the batteries are loaded. Certainbatteries also vary in output voltage with variations in temperature.Even under conditions where the battery voltage is not varying, thebattery may provide power at a different voltage than that required byuser devices.

Charge pumps are known circuits that effectively transfer electricalcharge back and forth between storage components to generate an outputvoltage different from an input voltage. Charge pumps with a “buck”feature are effectively voltage limiters. If the input voltage exceeds athreshold value, the charge pump “bucks” the overvoltage away from theload. However, in a charge pump circuit, the charge is not simplyshunted to ground or another load as in, for example, zener diodecircuits. A charge pump temporarily stores the charge redirected fromthe load, typically in a capacitive element. This charge stored in thecapacitor is then typically delivered to the load at a later time. Zenerdiodes are effective at clamping voltages above a certain threshold;however, by simply shunting the current away from the load, the currentis typically not available for use. This results in wasted power. Itwill be appreciated that wasting power in a device with limited batterycapacity is preferably avoided.

In a “boost” operation, a charge pump accumulates charge to be able toprovide a greater voltage to the load than is provided by the inputvoltage. A charge pump in boost operation typically sequentially chargesat least one capacitor connected in parallel with the power source andthen selectively interconnects the capacitor(s) in series with powersource to increase the available voltage for delivery to the load.Typical charge pump circuits double or triple the input voltage minussome switching and other loses. Again, it will be appreciated thatminimizing loses from a limited power source such as a battery isdesirable.

Charge pump circuits are often used in consumer electronics, such asPDAs, cell phones, and the like. Thus, it will be appreciated thatsimplicity and low cost are highly desirably. With potential markets inthe millions of units, a reduction in cost of only a few cents can addup to significant savings and increased profits for the manufacturersand sellers. An additional design goal is to reduce size and weight ofthe devices. Reduced size and weight increases the convenience of anappliance to the consumer and increases the marketability of theappliance. Many known charge pump designs employ multiple operatingmodes that increase circuit complexity and cost of the charge pumps.Multiple operating modes also generally lead to voltage transients uponswitching between the multiple modes, which again can damage powereddevices.

An additional problem with the charge pump circuits is that theconversion efficiency declines very quickly when the output voltage isless than twice the input voltage. The general rule for any charge pumpis that input current will always be twice the output current when thecircuit is in equilibrium. Current is drawn from the battery on everyclock cycle; however, it is only supplied to the load every other clockcycle. Thus, the instantaneous current is the same in the input andoutput sides, but the time average current for the input is twice theoutput. Since efficiency is the ratio of power out divided by power in,and input current is always twice output current, the maximumtheoretical efficiency can be calculated as follows:

Eff=Pout/Pin

Eff=(Iout×Vout)/(Iin×Vin)

Eff=(Iout×Vout)/(2×Iout×Vin)

Eff=(Vout/(2×Vin))×(100%)

Therefore:

Eff=100% max when Vout=2 Vin

Eff=50% max when Vout=Vin

Eff=25% max when Vout=½ Vin

In practical circuits, it is reasonable to expect 10% losses in theconverter because of resistive losses in switching components andjunction drops. The actual predictions made by multiplying thetheoretical predictions above by 90% are 90%, 45% and 22%, respectively.

One reason for the low efficiency numbers when Vout is <2 Vin is thatthe charge current for the transfer capacitor Cx flows from the batterydirectly to ground without imparting its full energy on Cx, (i.e., Cx isnot charged to the battery's full potential). Thus, the voltagedifference between the available battery potential and the voltageneeded to charge Cx to obtain the desired output voltage is available,but is not utilized.

Many real world battery-powered applications that include multiple loadswith different power requirements and meet the criteria for using asecondary load output from the charge pump. For example, cellulartelephones and handheld computers (PDAs) are typically powered by singlecell Lithium-ion or triple cell NiCad batteries having terminal voltagesthat range from 5.6 volts at full charge to 3.0 volts at cutoff. Acommon requirement in these products is to provide one regulated outputvoltage in the 5-volt to 3.3-volt range and to provide a secondregulated output voltage in the 2.5-volt 1.5-volt range.

A very specific application in the cellular phone product area isdriving a combination of white and green LEDs that light a color displayand a keypad. White LEDs are needed to provide good color from a liquidcrystal thin film transistor (TFT) display. These white LEDs typicallyhave forward voltage drops of 3.6V and draw approximately 20 mA each.Therefore. the white LEDs require a buck/boost voltage converter tooperate from the normal 5.6-volt to 3.0-volt battery potential. Anadditional requirement for the white LEDs is that all the LEDs generateapproximately the same light intensity in order to achieve uniformlighting in the display.

The cell phone also uses a lighted key pad, but this can use lower costand lower voltage green LEDs. Uniformity of lighting and color truenessof the keypad is less of a concern than with the display. Green LEDsoperate at 2.0 volts at 10 mA drive levels, thus using less power perLED (≈20mW) than white LEDs (≈72mW). However, because the electricalrequirements of green and white LEDs differ, two separate circuits aretypically required to enable to advantages of using green and whiteLEDs.

In order to maintain a constant and consistent light output, multipleLEDs require a constant current rather than constant voltage. One methodof driving LEDs is to use a constant voltage source with currentlimiting ballast resistors in series with the LEDs to sense and/orcontrol forward current. Multiple LEDs can be driven in parallel or inseries. If in series, only one series resistor is required for the LEDsin that branch, however the supply voltage must be high enough tosupport the sum of the forward voltages of the LEDs. Unfortunately, thevoltage required for two or more LEDs is higher than readily achievablewith a switched capacitor charge pump fed by a typical battery.

When multiple LEDs are driven in parallel, the supply voltage only needsto be in the 4V range, which is easily achievable with a charge pumpoperating from a 3-volt battery. In the parallel case, each LED has itsown series resistor to control and balance its current. However, thisapproach has two weaknesses:

1) Current matching among the LEDs is needed to insure equal lightoutput. Individual LEDs will have different forward voltage drops atequal drive currents. Because of this, the value of a series ballastresistor must be fairly high to control current sharing withoutundertaking the significant time and expense of testing and selectingLEDs for minimal variations in forward voltage. Typically, dropping atleast one-fourth of the forward voltage of the LEDs would be needed tomaintain less than 10% current variation among the multiple LEDs. With aprimary supply voltage of 3.0 volts providing power to a charge pumppowering white LEDs with 3.6-volt forward voltage drops, 0.9 volts wouldtypically be needed across the series resistor to achieve less than 10%current variation. This would result in a 20% loss because one-fifth ofthe total supply voltage is used in the ballast resistor and energy islost to resistive heating rather being used for the desired lightproduction.

2) The product would be burdened with the extra space and cost of theseries resistors.

Thus, from the foregoing it will be appreciated that there is a need foran efficient charge pump that provides both buck and boost operationsand that provides an output voltage that is regulated to provide astable output voltage even in the presence of variations in an inputvoltage. A need also exists for a regulating charge pump of simpledesign that avoids the cost and complexity of multiple operating modes.A need also exists for a charge pump that avoids switching betweenmultiple operation modes and that minimizes switching transients.Furthermore, a need exists for a buck/boost capable charge pump that canprovide regulated outputs at different voltage levels with a singlecircuit. Advantageously, such a multiple output regulating charge pumpoperates with improved efficiency. Moreover, a need exists for a singlecircuit that provides multiple voltage regulated outputs and that alsoregulates the current in multiple branches of at least one of theoutputs so as to facilitate powering LEDs in a highly efficient andbalanced manner.

SUMMARY OF THE INVENTION

One aspect of the present invention solves these and other problems byproviding a single mode buck/boost charge pump that provides a regulatedconstant output voltage between zero and twice an input voltage withoutchanging control modes or interrupting circuit operation when the inputvoltage falls below or rises above a set output voltage. In oneembodiment, a single mode buck/boost charge pump is adapted to power aplurality of separate loads in a highly efficient manner. In anotherembodiment, a single mode buck/boost charge pump is a combinationcurrent regulator and multiple output regulating charge pump adapted fordriving LEDs in a highly efficient and balanced manner.

In one aspect of the present invention, a regulating charge pumpprovides buck and boost operation in a single operating mode wherein thecharge pump provides an output voltage that is a multiple of anindependent reference voltage and wherein a charge storage component ischarged by a regulated variable current supply. In one embodiment, thevariable current supply is regulated with respect to the referencevoltage and the output voltage and the charge storage component isalternately charged by the regulated variable current supply andconnected in series with the output. In certain embodiments, the chargestorage component is inhibited from being charged when connected inseries with the output.

In certain embodiments, the reference voltage is a fixed voltage, and inalternative embodiments, the reference voltage is selectable from amonga plurality of voltage values.

In another aspect of the present invention, a regulating charge pumpreceives a supply voltage and provides a regulated output voltage. Thecharge pump comprises a charge storage component, a plurality ofswitches interconnecting the charge storage component and the supplyvoltage, a switch timing control that regulates the states of theplurality of switches, a reference voltage source, an error amplifierconnected to the reference voltage source and the regulated output, anda variable current supply that receives control signals from the erroramplifier and provides regulated current to the charge storage componentin response to the output voltage, wherein the output voltage isregulated with respect to the reference voltage source. In particularembodiments, the switch timing control alternately connects the chargestorage component to the variable current supply and in series with theregulated output. In certain embodiments thereof, the switch timingcontrol inhibits connecting the charge storage component to the variablecurrent source and the output simultaneously. The switch timing controloperates in a periodic fashion.

In certain embodiments, the reference voltage is a fixed voltage. Inalternative embodiments, the reference voltage is selectable from amonga plurality of voltage values. In other embodiments, the error amplifiercomprises a feedback network and in certain embodiments thereof, thefeedback network comprises a voltage divider connected to the regulatedoutput.

In a further aspect of the present invention, a method provides a stableoutput voltage. The method comprises providing an input voltage andproviding a reference voltage. The method sequentially charges a chargestorage component via a regulated variable current source and connectsthe charge storage component in series with the input voltage so as togenerate the output voltage. The method monitors the output voltage andregulates the charging of the charge storage component such that theoutput voltage is a multiple of the reference voltage.

In one embodiment, the present invention is useful in charge pumpapplications where a supply voltage, Vin, is higher than a minimumsupply voltage needed to provide the output voltage Vout. Thus, thecharge component is not charged to a maximum value that it can reach.The difference between the minimum supply voltage and the maximumvoltage on the charge storage component is used to generate a secondvoltage output from the circuit. The second voltage output is suppliedto a second, separate load. In this aspect, the present invention isable to supply different multiple regulated outputs from a single inputvoltage. In certain embodiments, the input voltage is lower than oneoutput voltage and higher than the other output voltage.

For example, at a minimum battery voltage of 3.0V, white LEDs require a0.6-volt boost, plus about 200 mV to implement a constant currentdriver. Thus, the minimum output voltage provided to white LEDs must beabout 3.9 volts to account for other circuit losses. The total boostrequired from a charge pump is then 3.9−3.0=0.9 volts. Since the minimumbattery voltage is 3.0 volts and the 0.9-volt boost must appear acrossthe charge transfer component while it is being charged, the differenceof 2.1 volts (3.0−0.9) is available to drive the second load. It iscommon to use four green LEDs operating at 10 mA to light the keypad.The remaining 2.1 volts is adequate to do this with 100 mV left over forcircuit losses. The total current required by two white LEDs isapproximately the same as required by the four green LEDs. This isadvantageous because virtually all of the unused energy from the chargepump can be diverted to the green LEDs. In addition, since both thewhite LEDs and the green LEDs are typically turned on at the same time,it is advantageous to share the same charge pump circuit.

In one aspect of the present invention, a charge pump receives a supplyvoltage wherein the charge pump provides multiple regulated outputs. Inone particular embodiment, the multiple regulated outputs are atdifferent voltages, and at least one of the multiple outputs isregulated at a voltage different than the supply voltage. In certainembodiments, the outputs are regulated independently with respect toinput voltage.

In another aspect of the present invention, at least one of the outputsis regulated with respect to a parameter of a load connected to the atleast one output. In one particular embodiment, the parameter of theload corresponds to an output node of the load. In another embodiment,regulating the at least one output with respect to the parameter of theload automatically compensates the at least one output for variations inthe parameter of the load. In this embodiment, the variations in theparameter of the load include variations due to temperature change.

In a further aspect of the present invention, a multiple outputregulating charge pump receives a supply voltage. The charge pumpcomprises a charge storage component, a plurality of switchesinterconnecting the charge storage component and the supply voltage, aswitch timing control that regulates the state of the plurality ofswitches, a reference voltage source, and a feedback circuit thatprovides regulated current to the charge storage component in responseto the output voltage, wherein the output voltage is regulated withrespect to the reference voltage source. In certain embodiments, themultiple outputs provide regulated voltages to at least a first load anda second load. In a particular embodiment, the output voltage is furtherregulated with respect to at least one of the first load and the secondload. In an embodiment thereof, the output voltage is regulated withrespect to an output node of at least one of the first load and thesecond load.

In yet another aspect of the present invention, the switch timingcontrol operates the switches so as to alternately charge and dischargethe charge storage component. In one embodiment, charging the chargestorage component comprises connecting the charge storage component inseries with the supply voltage and the second load, and discharging thecharge storage component comprises connecting the charge storagecomponent in series with the supply voltage and the first load. In acertain embodiment, current is provided to the first load as the chargestorage component is discharged and is provided to the second load asthe charge storage component is charged. In another embodiment, theswitch timing control operates the switches so as to inhibit having thecharge storage component connected in series with the supply voltage andboth the first and the second loads simultaneously.

In particular embodiments of the invention, the feedback circuitcomprises a variable current source and an error amplifier and thevoltage reference provides a fixed reference voltage. In a furtherembodiment, the reference voltage is selectable among a plurality ofreference voltage values.

In one embodiment, a multiple output regulated charge pump is combinedwith constant current sinks for multiple white LEDs to provide an LEDdriver and a load current regulator with higher efficiency. This alsoresults in a lower component count. In addition, a greater accuracy canbe obtained for cell phone and PDA applications that must operate frombatteries having voltages that range from 3.0 volts to 5.6 volts. Thedevice is scaleable to different quantities of LEDs by simply adding acurrent sink for each additional white LED in the application. The loadcurrent regulator is capable of maintaining less than 10% currentvariation among the white LEDs with only a 300 mV overhead andeliminates the need for ballast resistors in the load.

In one aspect of the present invention, a multiple output regulatingcharge pump receives a supply voltage and provides at least a firstregulated output and a second regulated output. The first regulatedoutput has a voltage that can be regulated at a level different than thevoltage of the supply, and the current provided to a load by the firstoutput voltage is actively current regulated. In certain embodiments,the first output is voltage regulated with respect to an output node ofthe load connected to the first output, thereby automaticallycompensating for variations in load characteristics.

One aspect of the present invention is a charge pump with a chargestorage component and a plurality of switches connected to the chargestorage component under control of a switch timing control circuit. Theswitch timing control circuit controls the switches to sequentiallyconnect the charge storage component to the supply in series with thefirst output and then in series with the second output. The chargestorage component is alternately charged when connected in series withthe second output and discharged when connected in series with the firstoutput so as to provide the first regulated output voltage. The switchtiming control operates to prevent the charge storage component beingconnected to both the first and the second outputs simultaneously. Incertain aspects of the invention, the switch timing control receivestiming signals from an oscillator such that the switch timing controlcircuit operates to open and close the switches in a periodic fashion.

In another aspect of the present invention, a current is supplied to aload connected to the second output when the charge storage component isbeing charged and at least the first output is voltage and currentregulated so as to provide substantially equal currents to multiplebranches of the load connected to the first output.

Another aspect of the invention is a load current regulator thatregulates the current provided to the load connected to the firstoutput. In particular, the load current regulator regulates the currentamong the multiple branches of the load connected to the first outputsuch that the current in each of the branches of the load issubstantially equal.

In certain embodiments, the load current regulator comprises a pluralityof transistors arranged in a current mirror configuration and the loadconnected to the at least first output comprises a light emitting diode.

A further aspect of the present invention is a regulating charge pumpthat receives a supply voltage and that provides regulated voltages toat least two loads. The charge pump comprises a charge storagecomponent, a variable current source, an error amplifier that receivesfeedback from at least one of the loads and provides control signals tothe variable current source, and a plurality of switches thatinterconnect the supply, the charge storage component, the variablecurrent source, the error amplifier, and the at least two loads. Aswitch timing control circuit controls the operation of the switchessuch that the variable current source can supply current to the chargestorage component and directly to at least one of the loads. A loadcurrent regulator is connected to at least one of the loads such thatcurrents within multiple branches of the load are actively balanced.

In certain embodiments, the error amplifier receives feedback from anoutput node of the at least one load. The switch timing control circuitoperates the switches such that the charge pump alternately providesregulated voltage to a first load as the charge storage componentdischarges and provides regulated voltage to a second load as the chargestorage component is charged.

In certain embodiments in accordance with the foregoing aspects of thepresent invention, the charge pump includes a switch timing controlcircuit that operates the switches in a periodic manner. The switchtiming control circuit prevents all the switches from being turned on atthe same time. The load current regulator comprises a plurality oftransistors arranged in a current mirror configuration.

The foregoing aspects of the present invention will become more fullyapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described in detail belowin connection with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of a typical prior art unregulated switchedcapacitor voltage doubler;

FIG. 2 is an equivalent circuit diagram of the circuit of FIG. 1 duringa charge half-cycle;

FIG. 3 is an equivalent circuit diagram of the circuit of FIG. 1 duringa discharge half-cycle;

FIG. 4 is a circuit diagram of one embodiment of a regulated buck/boostcharge pump of the present invention;

FIG. 5 is an equivalent circuit diagram of the regulated charge pump ofFIG. 4 during a charge half-cycle;

FIG. 6 is an equivalent circuit diagram of the regulated charge pump ofFIG. 4 during a discharge half-cycle;

FIG. 7 is a timing diagram of one embodiment of a switch timing control;

FIG. 8 is a circuit diagram of one embodiment of a switch timingcontrol;

FIG. 9 is a circuit diagram of one embodiment of a multiple outputcharge pump;

FIG. 10 is an equivalent circuit of the multiple output charge pump ofFIG. 9 during a charge half-cycle;

FIG. 11 is an equivalent circuit diagram of the multiple output chargepump of FIG. 9 during a discharge half-cycle;

FIG. 12 is a circuit diagram of an alternate embodiment of a multipleoutput charge pump;

FIG. 13 is a circuit diagram of a charge pump with load currentregulation;

FIG. 14 is a circuit diagram of the charge pump with load currentregulation of FIG. 13 during a charge half-cycle, providing power to asecond load;

FIG. 15 is a circuit diagram of the charge pump with load currentregulation of FIG. 15 during a discharge half-cycle providing regulatedvoltage and current to multiple branches of a first load; and

FIG. 16 is a detailed circuit diagram of the charge pump with loadcurrent regulation of FIG. 13.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the drawings wherein like numerals referto like parts throughout. FIGS. 1-3 illustrate a typical prior artcharge pump voltage doubler circuit. The charge pump circuit includesfour semiconductor switches, S1-S4, represented in the drawings assingle-pole, single-throw (SPST) switches. The four switches arecontrolled to alternately connect a charge transfer capacitor, C_(x), inparallel with a source supply (e.g., a battery) during a charge halfcycle illustrated in FIG. 2, and to then connect the charge transfercapacitor, C_(x), in series with the supply and a load during adischarge half cycle illustrated in FIG. 3. A load resistor, R_(load),is connected in parallel with an output capacitor, C_(out). The outputcapacitor stores energy transferred from the transfer capacitor, C_(x),during the discharge half cycle in FIG. 3 and transfers the energy tothe load during the charge half cycle in FIG. 2. The odd numberedswitches, S1 and S3, are closed during the charge half cycle (FIG. 2),and the even numbered, S2 and S4, are closed during the discharge halfcycle (FIG. 3). A square wave oscillator generates a timing signal to aswitch timing control circuit. The switch timing control circuitgenerates control signals to the four switches that determine when theswitches are opened and closed. The switch timing control circuit turnsoff the switches S1 and S3 before turning on the switches S2 and S4.Similarly, the switch timing control circuit turns off the switches S2and S4 before turning on the switches S1 and S3. This “dead time”between the opening of one pair of switches and the closing of the otherpair of switches prevents both sets of switches from being on at thesame time.

In the following discussion, the following relationships between theelements in FIGS. 1-3 are assumed:

C_(x) charge time=C_(x) discharge time

C_(x) charge current>C_(x) discharge current during start up.

C_(x) charge current=C_(x) discharge current during steady stateoperation.

Voltage across C_(x)=Voltage across V_(in)

V_(out)≈2×V_(in)

In FIG. 2, when S1 and S3 are closed, the semiconductor switches have onresistances of approximately 5 ohms and are represented by resistorsR_(S1) and R_(S2), respectively. Using this representation, it can beseen that:   C _(x) charge current=[V _(IN)/(R _(S1) +R _(S3))]×[e^(−t/RC)],

where RC=(R_(S1)+R_(S3))(C_(x))

In FIG. 3, S2 and S4 are closed and are represented by 5-ohm resistors,R_(S2) and R_(S4), respectively. Thus, it can be seen that:

C _(x) discharge current=[(VIN−VOUT)/(R _(S2) +R _(S4))]×[e ^(−t/RC)],

where RC=(R_(S2)+R_(S4))×(C_(x)),

and where C_(out)>>C_(x).

In the configuration illustrated in FIGS. 1-3, the output voltage,V_(out), is a function of the input voltage, V_(in), and is determinedboth by circuit component values and by V_(in). Thus, the output voltagewill vary with the input voltage. As previously mentioned, variations inthe output voltage of a charge pump can have deleterious effects onother circuits and components receiving power from the charge pump.

FIG. 4 illustrates one embodiment of a regulating charge pump 100 inaccordance with the present invention. The regulating charge pump 100receives electrical power from a primary power source 102 and provides aregulated output in a manner that will be described in greater detailbelow. In certain embodiments, the power source 102 comprisessingle-cell Lithium-ion or 3-cell Nickel-Cadmium (NiCad) batteries oftypes well known in the art. The power source 102, in one embodiment,provides input power on a terminal 103 at a voltage V_(in) that variesfrom approximately 5.6V at full charge to approximately 3.0V at cutoff.

The regulating charge pump 100 also comprises semiconductor switches(S1) 104, (S2) 106, (S3) 110 and (S4) 112. The switches 104 and 106 haverespective first terminals that are connected to the power source 102. Asecond terminal of the switch 104 is connected to a first terminal ofthe switch 112. A second terminal of the switch 112 is connected to anoutput terminal 142 that provides an output voltage, V_(OUT). The secondterminal of the switch 112 is also connected to a first terminal of aresistor 132. A second terminal of the switch 106 is connected to afirst terminal of the switch 110. A second terminal of the switch 110 isconnected to a variable current source 122, discussed below.

The regulating charge pump 100 also comprises a charge storage deviceC_(x) 114 that is connected between a node V_(CX1) and a node V_(CX2).The node V_(CX1) is connected to the second terminal of the switch 104and to the first terminal of the switch 112. The node V_(CX2) isconnected to the second terminal of the switch 106 and to the firstterminal of the switch 104. In one embodiment, the charge storage deviceC_(x) 114 comprises a non-polarized capacitor of 1 μF of a type wellknown in the art. As discussed above in connection with FIGS. 1-3, thecharge storage device C_(x) 114 of FIG. 4 temporarily stores anelectrical charge to enable the regulating charge pump 100 to deliver anoutput V_(out) on the node 142 in a manner that will be described ingreater detail below.

The regulating charge pump 100 also comprises a switch timing controlcircuit 116. The switch timing control circuit 116 generates timingsignals T1 172 and T2 174 (illustrated in FIGS. 7 and 8) to control theswitching of the switches 104, 106, 110, and 112 in a manner that willbe described in greater detail below. In a preferred embodimentdescribed herein, the switch timing control circuit 116 controls theswitches 104 and 110 to operate in concert as a first pair of switchesand controls the switches 106 and 112 to operate in concert as a secondpair of switches. In particular, the switches 104 and 110 are closed andopened together, and the switches 106 and 112 are closed and openedtogether. As discussed above, the complementary closing and opening ofthe switches 104 and 110 with respect to the switches 106 and 112 isregulated by the switch timing control circuit 116 such that theswitches 104 and 110 open completely before the switches 106 and 112 areclosed and such that the switches 106 and 112 open completely before theswitches 104 and 110 are closed to thereby prevent both pairs ofswitches from being closed simultaneously.

The regulating charge pump 100 also comprises a conventional square-waveoscillator 120. In the preferred embodiment, the square-wave oscillator120 generates a square-wave signal F_In 170 (FIG. 7) that has afrequency of approximately 500 kHz. The square-wave oscillator 120provides a timing clock to the switch timing control circuit 116. Theswitch timing control circuit 116 generates the T1 control signal 172and the T2 control signal 174 in synchronism with the timing clock toprovide the timing control signals for the opening and closing of theswitch pairs 104 and 110 and 106 and 112.

As shown in FIG. 7 for the preferred embodiment, the T1 signal 172 issubstantially in phase with the F_In signal 170; however, the risingedge of the T1 signal 172 lags the rising edge of the F_In signal 170 byapproximately 60 nanoseconds. The falling edge of the T1 signal 172occurs substantially synchronously with the falling edge of the F_Insignal 170. The T2 signal 174 is substantially 180° out of phase withthe F_In signal 170 such that the rising edge of the F_In signal 170occurs synchronously with the falling edge of the T2 signal 174. Therising edge of the T2 signal 174 lags the falling edge of the F_Insignal 170 by approximately 60 nanoseconds. Thus, both the T1 signal 172and the T2 signal 174 are high for alternating 940-nanosecond periods ata frequency of approximately 500 kHz with 60-nanosecond null periodsinterposed between the active periods of the T1 signal 172 and the T2signal 174. Thus, the switch pairs 104, 110 and 106, 112 are closed foralternating 940-nanosecond periods with 60 nanoseconds of dead timebetween each closed period.

FIG. 8 is a circuit diagram of one embodiment of the switch timingcontrol circuit 116. The switch timing control circuit 116 receives theF_In signal 170 on an input terminal, as previously described. A 50 Ωresistor R7 176 is connected between the input terminal and circuitground 130. The F_In signal 170 is also coupled to the input of aninverter 180. The output of the inverter 180 is connected to both inputsof an AND gate 182 and to a first input of an AND gate 184. The outputof the AND gate 182 is connected to a second input of the AND gate 184with a delay circuit 194 interposed therebetween. The delay circuit 194of this embodiment comprises a resistor R9 connected between the outputof the AND gate 182 and the second input of the AND gate 184 and acapacitor C3 connected between the second input of the AND gate 184 andthe circuit ground. The component values of the delay circuit 194 areselected to provide a 60-nanosecond delay between the output of theinverter 180 and the second input of the AND gate 184. The output of theAND gate 184 generates the T2 signal 174. Thus, a rising edge of theF_In signal 170 causes an immediate falling edge of the T2 signal 174. Afalling edge of the F_In signal 170 causes a rising edge of the T2signal 174 after a delay of approximately 60 nanoseconds.

The switch timing control circuit 116 of this embodiment also comprisesan AND gate 186 having both inputs connected directly to the inputterminal to receive the F_In signal 170. The F_In signal 170 is alsoconnected to a first input of an AND gate 190. A delay circuit 192,comprising a resistor R8 and a capacitor C2, is also interposed betweenthe output of the AND gate 186 and the second input of the AND gate 190in a comparable manner to that previously described with respect to thedelay circuit 194. The output of the AND gate 190 generates the T1signal 172. A falling edge of the F_In signal 170 causes an immediatefalling edge of the T1 signal 172 on the output of the AND gate 190. Arising edge of the F_In signal 170 causes a rising edge of the T1 signal172 after a delay of approximately 60 nanoseconds through the delaycircuit 194.

In the illustrated embodiment of the switch timing control circuit 116,the inverter 180 is advantageously a type 74ACT11240 integrated circuit,and each AND gate 182, 184, 186, 190 is advantageously a type 74ACT08integrated circuit. In this embodiment, the delay circuits 192, 194 eachcomprise a 200% resistor and a 200 pF capacitor. It will be appreciatedthat other component values and types can be incorporated foralternative embodiments without detracting from the spirit of thepresent invention as described in this embodiment.

As further illustrated in FIG. 4, the regulating charge pump 100 alsocomprises a variable current source 122. The variable current source 122is connected to the second terminal of the switch 110 to selectivelyprovide a regulated current IS1 156 to the charge storage component,C_(x), 114 in a manner that will be described in greater detail below.The variable current source 122 in this embodiment is capable ofsourcing or sinking the regulated current IS1 156 at a magnitude up toapproximately 100 mA.

The regulating charge pump 100 also comprises an error amplifier 124.The amplifier 124 is connected to the variable current source 122 toregulate the current supplied by the variable current source 122 to thecharge storage component 114 via switch 110 in response to a feedbacksignal from the output voltage generated by the regulating charge pump100. In this embodiment, the amplifier 124 is an operational amplifier(OpAmp) of a type well known in the art.

A voltage reference 126 is connected between the non-inverting input ofthe amplifier 124 and the circuit ground 130. In this embodiment, thevoltage reference 126 provides a fixed 1.0 volt DC signal. Inalternative embodiments, the voltage reference 126 provides a variablesignal. For example, the voltage reference 126 is advantageouslyselectable among a plurality of fixed values.

The regulating charge pump 100 also comprises a resistor (R1) 132 and aresistor (R2) 134. As discussed above, the first terminal of theresistor 132 is connected to the second terminal of the switch 112. Asecond terminal of the resistor 132 is connected to the inverting inputof the amplifier 124 and also to a first terminal of the resistor 134.The second terminal of the resistor 134 is connected to the circuitground 130. In this embodiment, the resistor 132 has a value ofapproximately 230 kΩ and the resistor 134 has a value of approximately100 kΩ.

The resistors 132 and 134 form a voltage divider 136 between the secondterminal of the switch 112 and the circuit ground 130, wherein thecommon connection between the two resistors is a voltage division nodethat is connected to the inverting input of the amplifier 124. Theamplifier 124, the voltage reference 126, and the voltage divider 136form a feedback circuit 140. The feedback circuit 140 provides controlinputs to the variable current source 122 in response to the voltage atthe second terminal of the switch 112.

The voltage at the second terminal of the switch 112 is also the outputvoltage, V_(OUT) on the node 142. The output voltage V_(OUT) on the node142 is provided to a load 400. In this embodiment, the load 400comprises a resistive component in parallel with a capacitive component.The resistive component of the load has a resistance of approximately 44Ω, and the capacitive component of the load has a capacitance ofapproximately 100 μF.

With the component values previously described for this embodiment, aV_(OUT) of 3.3 volts on the node 142 generates a voltage at the voltagedividing node of the voltage divider 136 and thus at the inverting inputof the amplifier 124 of approximately 3.3×(100/(100+230)) volts=1 volt,which is the same value of the voltage reference 126 as provided to thenon-inverting input of the amplifier 124. Thus, it will be appreciatedthat a V_(OUT) of 3.3 volts on the terminal 142 will generate a minimalfeedback signal from the feedback circuit 140 and thus induce a steadystate current from the variable current source 122. When V_(OUT) on theterminal 142 is not equal to 3.3 volts, the feedback circuit 140 willsource or sink a regulated current IS1 to attempt to return the voltageV_(OUT) on the terminal 142 to 3.3 volts in a manner that will bedescribed in greater detail below.

The regulated charge pump 100 may be considered to include a simulatedvariable battery (C_(x)) that can assume any DC voltage from +V_(IN) to−V_(IN). The simulated battery can be alternately connected in parallelor in series with the power source 102. When in series, the simulatedbattery supplies current to the load along with the power source 102.When in parallel, the simulated battery is recharged. The absolute valueand polarity of the DC voltage across C_(x) is determined by themagnitudes of the input and output voltages so that the followingequations are met:

V _(OUT) =V _(IN) +V _(CX)

V _(CX) =V _(OUT) −V _(IN)

In one embodiment, with V_(OUT)=3.3 volts and V_(IN)=3.0 volts, thenV_(Cx)=+0.3 volts (i.e., V_(Cx1)=V_(Cx2)+0.3 volts).

If V_(OUT)=3.3 volts and V_(IN)=6.0 volts, then V_(Cx)=−2.7 volts

(i.e., V_(Cx1)=V_(Cx2)−2.7 volts).

The dynamics of this simulated battery voltage are defined by thefollowing equations:

Q=I×T=CV

V=I×T/C

where Q is the charge in Coulombs, I is current in amperes, T is time inseconds, C is the value of C_(x) in Farads, and V is the voltage acrossC_(x). If the incremental charge and discharge currents in C_(x) arerelatively small and if C_(x) is relatively large, the incremental orripple voltage on C_(x) will be small. This condition makes thesimulated battery look very much like an actual battery.

Under steady-state operation, where the average values of V_(in),V_(out) and current in the load do not change, the charging current toC_(x) must equal its discharging current in order to maintain a constantDC voltage across C_(x). In this simulated battery, if the averagecharge current over many pump cycles exceeds the discharge current, apositive voltage (V_(Cx1)>V_(Cx2)) will develop across C_(x). On theother hand, if average discharge current is greater, a negative voltageresults (V_(Cx1)<V_(Cx2)). The feedback circuit 140, as shown in FIG. 4,forces an imbalance of current in the charge storage component, C_(x),114 to adjust its steady-state voltage whenever input voltage or loadcurrent changes.

Also, since the charge current in C_(x) has a maximum value determinedby design, and since I_(OUT) cannot exceed I_(IN) in this topology(under steady-state conditions), the output is automatically shortcircuit current limited.

FIG. 5 is an equivalent circuit diagram of one embodiment of theregulating charge pump 100 during start-up conditions. For illustrationpurposes, the initial conditions are assumed to be:

V_(IN)=V_(OUT)=V_(Cx)=0 volts

C_(out)=100 μF

Cx=1 μF

Fosc=500 kHz

V_(out) is set to regulate to 3.3 volts into a 44-ohm load.

IS1≦100 mA (maximum).

Resistance of each switch 104, 106, 110, and 112=5 ohms

At power on in this embodiment, V_(IN)=6.0 V. When the oscillator 120starts, the arbitrary assumption will be made that the odd switch pair104 and 110 will close first as shown in FIG. 5. This places the chargestorage component C_(x) in series with the power source 102 and thevariable current source 122. Thus, a direct current will be provided bythe power source 102 to the charge storage component C_(x). This currentwill flow to cause the charge storage component C_(x) to gain a smallpositive voltage. Since V_(OUT)=0 volts at startup, the voltage at thevoltage division node 136 of the feedback circuit 140 is also 0 volts.Thus, the feedback loop 140 is unsatisfied, and the output of thevariable current source 122 will seek its maximum value, which in thisembodiment is approximately 100 mA. The circuit values will be definedby the equation:

ΔVCx ₁ =I×t/C

which in this embodiment will give values of

ΔVCx ₁=100 mA×1 μs/1 μF=+100 mV

FIG. 6 illustrates a subsequent clock cycle, wherein the charge storagecomponent C_(x) 114 is connected in series with the power source 102 andthe load 400 via the closed switch pair 106 and 112. Only the switch 106and the switch 112 on resistances (approximately 5 Ω each in thisembodiment) and the load 400 impedance limit discharge current. Theimpedance of the load 400 is negligible under transient conditionsbecause of the relatively high capacitance (100 μF) of C_(OUT). Thecircuit values will be defined by the equations:

ΔVCx ₂ =i×t/C, i=V/R×e ^(−t/rc)

ΔVCx ₂=((V _(IN) +V _(Cx) −V _(OUT))/2R _(switch))×(e ^(−t/rc))×(t/C)

In this embodiment, the corresponding component values will produce:

ΔVCx ₂≈((6+0.1−0)/10 Ω)×e ^(−1 μS/10 Ω×1 μF)(1 μS/1 μF)

≈0.61 volts×0.95≈0.580 volts

Since discharge current in the charge storage component C_(x) 114 duringthe second half cycle (FIG. 6) flows in the opposite direction to thecharge current in the first half cycle (FIG. 5), the voltage developedacross the charge storage component C_(x) 114 in the second half cycleis negative with respect to the first half cycle. Therefore, the newvalue for V_(Cx) is:

V _(Cx)(new)=V _(Cx1) +V _(Cx2)=+0.1−0.580=−0.480 volts

In subsequent cycles V_(out) on the terminal 142 will rise exponentiallytoward 3.3 volts while V_(Cx) charges to −2.7 volts DC. When equilibriumis reached, V_(OUT) will be approximately 3.3V, V_(IN) will beapproximately 6 volts and V_(Cx) will be approximately −2.7V. Thecurrent supplied to the load 400 under steady-state conditions is 3.3volts/44 Ω=75 mA. The charge and discharge currents for the chargestorage component C_(x) 114 are also 75 mA average (150 mA peak), andthe current I_(IN) delivered by the power source 102 is 150 mA average.The peak-to-peak ripple voltage across V_(Cx), assuming an equivalentseries resistance (ESR) of C_(x) is negligible, is 75 mA×1 μS/1 μF=75mV.

From an efficiency viewpoint, the foregoing example is nearly a worstcase since both I_(IN) and V_(IN) are larger than I_(OUT) and V_(OUT).In this example:

Eff=POUT/PIN=3.3×0.075/6×0.150

=27.5%, excluding FET resistive losses.

A similar example can be made for the case where V_(IN) is 3.0V. In thiscase, C_(x) will also initially charge in a negative direction, but willbecome zero when V_(OUT) reaches V_(IN), and will finally change to+0.3V.

FIG. 9 is a circuit diagram of one embodiment of a multiple outputregulating charge pump 900 (e.g., a dual output charge pump). In oneembodiment, the dual output charge pump 900 is the charge pump shown inFIG. 4 with a second load 152 interposed between the variable currentsource 122 and circuit ground 130. The dual output charge pump 900receives electrical power from a primary power source 102. In thisembodiment, the charge pump 900 provides a first regulated outputV_(OUT1) on the terminal 142 and provides a second regulated outputV_(OUT2) on a terminal 144 in a manner that will be described in greaterdetail below.

In the embodiment of FIG. 9, V_(OUT1) on the terminal 142 is regulatedat approximately 3.9 volts. V_(OUT1) is provided to a first load 146.The first load 146 advantageously comprises a capacitive component ofapproximately 10 μF in parallel with a plurality of white light emittingdiodes (LEDs) 150, with each LED 150 in series with a respectiveresistor (R3) 162 and (R4) 164.

The second output voltage V_(OUT2) on the terminal 144 is provided to asecond load 152. In this embodiment, V_(OUT2) is regulated to provideapproximately 40 mA of current to the second load 152. In the embodimentof FIG. 9, V_(OUT2) is the voltage present at the sink pole of thevariable current source 122. The second load 152 comprises a pluralityof green LEDs 154 connected in parallel between the terminal 144 andcircuit ground 130 so that the voltage V_(OUT2) appears across eachgreen LED.

In the embodiment of FIG. 9, the second load 152 is interposed betweenthe variable current source 122 and circuit ground 130. The regulatedcurrent 156 flowing from the variable current source 122 is provided tothe second load 152 at a voltage determined by the difference betweenthe voltage V_(IN) developed by the power source 102 and thesteady-state charge on the charge storage component 114.

As discussed above in connection with the charge pump 100 in FIG. 5, theregulated charge pump 900 in FIG. 9 may also be considered as includinga simulated variable battery (C_(x)) that can assume any DC voltage from+V_(IN) to −V_(IN). The simulated battery can be alternately connectedin series with the power source 102 and the first load 146 or with thesecond load 152. When in series with the first load 146, it suppliescurrent to the first load 146 along with the power source 102. When inseries with the second load 152, it is recharged. The absolute value andpolarity of DC voltage across C_(x) is determined by the magnitudes ofthe input and output voltages so that the following equations are met:

V _(OUT1) =V _(IN) +V _(CX)

V _(CX) =V _(OUT1) −V _(IN)

In one embodiment, with V_(OUT)=3.9 volts and V_(IN)=3.0 volts,

then V_(Cx)=+0.9 volts (i.e., V_(Cx1)=V_(Cx2)+0.9 volts).

If V_(OUT)=3.9 volts and V_(IN)=5.6 volts, then V_(Cx)=−1.7 volts

(i.e., V_(Cx1)=V_(Cx2)−1.7 volts).

FIG. 10 is an equivalent circuit of the dual output charge pump 900 ofFIG. 9 during a charge half-cycle, wherein current is supplied to thesecond load 152. In this embodiment, V_(IN)=3.0 volts, and the arbitraryassumption is made that the odd switches 104 and 110 are closed. Thisplaces the charge storage component C_(x) 114 in series with the powersource 102, the variable current source 122, and the second load 152. Tomaintain V_(OUT1) on the terminal 142 at 3.9 volts with V_(IN) on theterminal 103 at 3.0 volts, a voltage of 0.9 volts is required across thecharge storage component 114. The difference of 2.1 volts is availableat the V_(OUT2) terminal 144. Thus, a regulated direct current 156 isprovided by the power source 102 to the charge storage component C_(x)114 through the variable current source 122 and to the second load 152at 2.1 volts.

In the embodiment of FIG. 10, each of the four green LEDs 154 draws 10mA of current thus requiring a total regulated current (IS 156) of 40mA. This current also causes the voltage across the charge storagecomponent C_(x) 114 to increase by 0.9 volts. The output voltageV_(OUT2) available at the terminal 144 has a magnitude of 2.1 volts,which is within the optimal range to power the green LEDs 154.

FIG. 11 is an equivalent circuit diagram of the dual output charge pump900 of FIG. 9 during a discharge half-cycle, wherein the charge storagecomponent C_(x) 114 is connected in series with the power source 102 andthe first load 146 via the closed switch pair 106 and 112. In thiscondition, the power source 102 provides current through the chargestorage component 114, which adds 0.9V to V_(IN) and provides the totalvoltage as the output voltage V_(OUT1) to the first load 146 via theterminal 142. In the embodiment of FIG. 11, each white LED 150 draws 20mA for a total regulated current of 40 mA from the terminal 142.

The embodiment of the multiple output regulated charge pump 900described herein is particularly advantageous because the currentsrequired for operation of the first load 146 and the second load 152 aresubstantially identical. Also, in the application of cell phones, PDAs,and the like, both the white LEDs 150 of the first load 146 and thegreen LEDs 154 of the second load 152 are normally on at the same time.It will be appreciated that to a user of the device, sequentiallyturning on the white 150 and green LEDs 154 for 1 μs periods at 500 kHzwill appear to be a seamless, continuous operation.

The overall system level efficiency, defined here as the powerdissipated in the LEDs 150, 154 neglecting loses in the ballastresistors 162, 164 and neglecting switch loses at the minimum inputvoltage level V_(IN) of 3.0 volts from the power source 102 is definedby:

Eff=Pout/Pin=(Pwhite+Pgreen)/Pin

Pout=3.6 V×40 mA+2.0 V×40 mA=224 mW

Pin=Vin×2Iout=3.0 V×80 mA=240 mW

Therefore,

Eff=224/240=93.3% (Theoretical maximum).

The actual realized efficiency will be about 84% after accounting forlosses on the charge storage component 114 and the resistances of theswitches 104, 106, 110, and 112.

This efficiency of the regulating charge pump 900 of FIG. 9 can becompared to the case where a comparable array of green and white LEDsare driven directly from a battery with two linear current sourcecircuits where:

Pin=(V _(IN)×2I _(OUT) _(—) _(WHT))+(V _(BAT) ×I _(GREEN))240+120 360 mW

Eff224/360=62.2% (Theoretical Maximum)

The actual efficiency of the green driver is approximately 80/120=66.7%.

The actual efficiency of a separate white LED driver is about 0.9×calculated maximum:

Eff Wht=0.9×(3.6×0.04/3.0×0.08)

=0.9×(0.144/0.240)

=0.9(60%)≈54%.

The overall combined efficiency of the two separate circuits isapproximately 62%. In addition, this alternative to the presentinvention requires two separate circuits, whereas the multiple outputregulated charge pump 900 of the embodiment in FIG. 9 offers improvedefficiency in a single circuit. Thus, the efficiency from a system pointof view is increased from approximately 62% to approximately 84% withthe embodiment of FIG. 9, and a saving of approximately 120 mW isobtained. In other words, the total power usage of the LEDs 150, 154drops from approximately 360 mW to approximately 240 mw. Thus, a savingsof 120/360=33.3% of total power of the LEDs is obtained. As previouslydiscussed, reduced power consumption and improved efficiency is highlydesirable in the art of battery-powered devices. The efficiency foralternative embodiments with different values of V_(IN) are set forth inthe following table.

Efficiency vs. Vin for a single multiple output regulated charge pump900 vs. dual single output charge pumps with linear regulators. TwoWhite LEDs at 20 mA each, Four Green LEDs at 10 mA each EfficiencySystem of single Efficiency Efficiency output Efficiency Of Single ofWhite of Green output multiple LED LED pump + output charge linearlinear regulated Vin pump regulator regulator Charge 103 Pin Pout A BA + B Pump 100 3.2 V 256 144 50.6% 60.4% 81.5% mW mW wht wht +128 +8868.7% — mW mW grn grn 3.6 V 288 144 45% 53.7% 72.5% mW mW wht wht +144+88 61% — mW mW grn grn 4.2 V 336 144 38.5% 46% 62.1% mW mW wht wht +168+88 52.3% — mW mW grn grn 5.6 V 448 144 28.9% 34.5% 46.6% mW mW wht wht+224 +88 39.2% — mW mW grn grn

FIG. 12 is a circuit diagram of an alternative embodiment of a multipleoutput regulating charge pump 1200 that includes compensation forvariations in a forward voltage drop V_(F) of a white LED 150. Theoverall functionality and operation of the regulating charge pump 1200is substantially similar to that of the regulating charge pump 900described above. Attention will be drawn to the differences between theregulating charge pumps 900 and 1200. The components comprising theregulating charge pump 1200 and the operation thereof can be assumed tobe otherwise substantially similar to that previously described withrespect to the regulating charge pump 900.

The regulating charge pump 1200 eliminates the resistor (R1) 132 and theresistor (R2) 134. Instead, in the embodiment of FIG. 12, directconnection is made between the inverting input of the error amplifier124 and the node between the resistor (R3) 162 and a first white LED150.

The embodiment of FIG. 12 is advantageous because the sense signal forthe feedback circuit 140 (i.e., the voltage present at the invertinginput of the error amplifier 124) is derived from the “output” of thewhite LED 150 comprising the first load 146. In contrast, in FIG. 9, thesense signal is derived from the “input” of the white LED 150 comprisingthe first load 146. The white LEDs 150 have the forward voltage dropV_(F) as is well known in the art. During use, the forward voltage dropV_(F) can change as the temperatures and currents of the white LEDs 150change. Thus, the embodiment of FIG. 12 more closely tracks the actualoperating condition of the white LEDs 150 than is obtained by trackingthe first output voltage V_(OUT1) on the terminal 142 directly.

FIG. 13 is a circuit diagram of a charge pump 1300 with load currentregulation. The charge pump 1300 receives electrical power from aprimary power source 102, and, in this embodiment, provides a firstregulated output V_(OUT1) on the terminal 142 and provides a secondregulated output V_(OUT2) on the terminal 144 in a manner that will bedescribed in greater detail below. The overall functionality andoperation of the regulating charge pump 1300 is substantially similar tothat of the regulating charge pump 1200 as previously described.Attention will be drawn to the differences between the regulating chargepumps 1200 and 1300 and the components comprising the regulating chargepump 1300. The operation thereof can be assumed to be otherwisesubstantially similar to that previously described with respect to theregulating charge pump 1200.

Like the charge pump 1200, the regulating charge pump 1300 eliminatesthe current sensing resistor (R3) 162 and the current sensing resistor(R4) 164. Instead, in the embodiment of FIG. 13, an active load currentregulator 163 replaces the current sensing resistors 162 and 164 formore efficient operation. The active load current regulator 163 causes afirst sink current (ISINK1) 190 to flow through the first white LED 150and causes a second sink current (ISINK2) 192 to flow through the secondwhite LED 150.

FIG. 14 is a circuit diagram of the charge pump 1300 with load currentregulation of FIG. 13 during a charge half-cycle, during which thecharge pump 1300 provides power to a second load 152. In thisembodiment, V_(IN)=3.0 volts, and the arbitrary assumption is made thatthe switches 104 and 110 are closed. This places the charge storagecomponent C_(x) 114 in series with the power source 102, the variablecurrent source 122, and the second load 152. To maintain V_(OUT1) on theterminal 142 at 3.9 volts with V_(IN)=3.0 volts, a voltage ofapproximately 0.9 volts is required across the charge storage component114. The 2.1 volt difference between V_(IN) and the voltage across thecharge storage component 114 is thus available at the V_(OUT2) terminal144. A regulated direct current 156 will be provided by the power source102 to the charge storage component C_(x) 114 through the variablecurrent source 122 and to the second load 152 at 2.1V.

In the embodiment of FIGS. 13 and 14, each of the four green LEDs 154draws 15 mA of current, which results in a total regulated current 156of 60 mA. This current also causes voltage across the charge storagecomponent C_(x) 114 to increase by approximately 0.9V. The outputvoltage available at the V_(OUT2) terminal 144 is approximately 2.1V andis within the optimal range to power the green LEDs 154.

FIG. 15 is a circuit diagram of the charge pump 1300 with load currentregulation of FIG. 13 during a discharge half-cycle during whichregulated voltage and current are provided to multiple branches of afirst load 146. The charge storage component C_(x) 114 is connected inseries with the power source 102 and the first load 146 via the closedswitch switches 106 and 112. In this condition, the power source 102provides current through the charge storage component 114, which adds0.9 volts to V_(IN). The total voltage is applied to the first load 146via the terminal 142. In this embodiment, each white LED 150 draws 30 mAof current for a total regulated current 156 of 60 mA.

The embodiment of the multiple output regulated charge pump 1300described herein is particularly advantageous in that the currentsrequired for operation of the first load 146 and the second load 152 aresubstantially identical. Also, in the application of cell phones, PDAs,and the like, both the white LEDs 150 of the first load 146 and thegreen LEDs 154 of the second load 152 are normally on at the same time.The 10 μF capacitive element connected in parallel with the two whiteLEDs 150 filters the current in the first load 146 such that the ISINK1current 190 and the ISINK2 current 192 are substantially continuous. Inalternative embodiments, the 10 μF capacitive element can be eliminatedto allow the ISINK1 current 190 and the ISINK2 current 192 to pulse at50% duty cycle and double amplitude; however, the light output of theseembodiments will be less than the embodiment described above.

The overall system level efficiency, defined here as the powerdissipated in the LEDs 150, 154 neglecting switch loses at the minimumV_(IN) of 3.0 volts provided by the power source 102 is defined by:

Eff=Pout/Pin=(Pwhite+Pgreen)/Pin

Pout=3.6 V×60 mA+2.0 V×60 mA=336 mw

Pin=Vin×2×Iout=3.0 volts×120 mA=360 mw

Therefore,

Eff=336/360=93.3% (Theoretical maximum).

The actual realized efficiency will be about 84% after accounting forlosses on the charge storage component 114 and the resistance of theswitches 104, 106, 110, and 112.

This efficiency of the regulating charge pump 1300 of FIG. 13 can becompared to the case where a comparable array of green and white LEDsare driven directly from a battery with two linear current sourcecircuits where:

Pin=(V _(IN)×2×I _(OUT) _(—) _(WHT))+(V _(BAT) ×I _(OUT) _(—)_(GRN))=360+180 540 mw

Eff336/540=62.2% (Theoretical Maximum)

The actual efficiency of the green driver is 120/180=66.7%.

The actual efficiency of a separate white LED driver is about 0.9×calculated maximum:

Eff _(WHT)=0.9×(3.6×0.06/3.0×0.12)

=0.9(0.216/0.360)

=0.9×(60%)≈54%

The overall combined efficiency of the two separate circuits isapproximately 62%. In addition, this alternative to the presentinvention requires two separate circuits, whereas the multiple outputregulated charge pump 1300 of this embodiment offers improved efficiencyin a single circuit. Thus, the efficiency from a system point of view isincreased from approximately 62% to approximately 84% with theembodiment of FIG. 13. A saving of approximately 180 mW is obtained. Inother words, the total power usage of the LEDs 150, 154 drops fromapproximately 540 mW to approximately 360 mw. Thus, a savings of180/540=33.3% of total power of the LEDs 150, 154 is obtained. Aspreviously discussed, reduced power consumption and improved efficiencyare highly desirable in the art. The efficiency for alternativeembodiments with different values of V_(IN) 103 are given in thefollowing table.

Efficiency vs. Vin for a single multiple output regulated charge pump1300 vs. dual single output charge pumps with linear regulators. TwoWhite LEDs at 30 mA each, Four Green LEDs at 15 mA each EfficiencySystem of single Efficiency Efficiency output Efficiency Of Single ofWhite of Green output multiple LED LED pump + output charge linearlinear regulated Vin pump regulator regulator Charge 103 Pin Pout A BA + B Pump 1300 3.2 V 384 216 50.6% 60.4% 81.5% mW mW wht wht +192 +13268.7% — mW mW grn grn 3.6 V 432 216 45% 53.7% 72.5% mW mW wht wht +216+132 61% — mW mW grn grn 4.2 V 504 216 38.5% 46% 62.1% mW mW wht wht+252 +132 52.3% — mW mW grn grn 5.6 V 672 216 28.9% 34.5% 46.6% mW mWwht wht +336 +132 39.2% — mW mW grn grn

The output voltage V_(OUT1) on the terminal 142 will typically be 3.9volts, but can increase or decrease as the forward voltage of the whiteLED 150 changes. This is important, because the regulating charge pump1300 of the embodiment of FIG. 13 uses minimum output power at alltimes. The forward ISINK1 current 190 and the forward ISINK2 current 192of the white LEDs 150 can easily be reduced by reducing the 150 mVreference voltage 206 on the OpAmp 194 of the load current regulator 163to provide a dimming feature. When the ISINK1 current 190 and the ISINK2current 192 decrease, the forward voltage drop V_(F) decreases. In thecircuit of FIG. 13, the output voltage V_(OUT1) on the terminal 142follows to provide the highest possible efficiency. Temperature effectson the forward voltage V_(F) are also automatically compensated.

The total current through the four green LEDs 154 will be identical tothe white LED 150 total current (60 mA), since in equilibrium, the Cxcharge current is equal to the discharge current. In the circuit of FIG.13, the green LED 154 current will flow only during the charge halfcycle. If a filter capacitor is added on the V_(OUT2) terminal 144 inparallel to ground, DC current will flow in the green LEDs 154 in asimilar manner to that previously described with respect to the whiteLEDs 150. Current sharing in the green LEDs 154 is of less concern thanthe white LEDs 150, since the green LEDs are generally used only toprovide back light for the cell phones keys. The white LEDs 150 are usedto backlight the color TFT display, and should have equal currents toprevent uneven lighting and uneven coloration of the display.

The circuit of FIG. 13 operates at various frequencies and values of thecharge storage component 114. In general, the charge storage component114 should have a high value, and the frequency of the square waveoscillator 120 should be as high as possible to keep the ripple voltageon the charge storage component 114 low. This will minimize losses inthe charge storage component 114 and will extend the dynamic range ofthe output voltage V_(OUT1) on the terminal 142 and the output voltageV_(OUT2) on the terminal 144 because the charge storage component 114ripple voltage will not limit the extremes of the input voltage V_(IN)on the input terminal 103, the output voltage V_(OUT1) on the terminal142 and the output voltage V_(OUT2) on the terminal 144. It should alsobe appreciated that the present invention is scalable to otherquantities of LEDs 150, 154 by adding or removing the N-FETs 196, 200 tothe current mirror in the load current regulator 163, described below.

FIG. 16 is a detailed circuit diagram of the charge pump 1300 with loadcurrent regulation of FIG. 13. FIG. 16 illustrates one embodiment of theswitches 104, 106, 110, 112 in greater detail. Each of the switches 104and S2 106 comprises a type 74ACT11240 inverter and a type NDS332PP-FET. The input of the inverter in the switch 104 receives the T1control signal 172, and the input of the inverter in the switch 106receives the T2 control signal 174. The output of the inverter in eachswitch 104, 106 is connected to the gate of the associated P-FET.

The switch 110 comprises a type 74ACT11240 inverter with the outputthereof connected to the gate of a type NDS332P P-FET. The switch 110also comprises two type 74ACT11240 inverters connected in series withthe output of the second inverter connected to the gate of a typeFDV303N N-FET. The type NDS332P P-FET and the type FDV303N N-FET areconnected as a parallel pair so that the first terminal of the switch110 floats above the circuit ground 130 without turning off the switch110. The inputs of the switch 110, corresponding to the inputs of theinverters, receives the T1 control signal 172.

The switch 112 comprises two type 74ACT11240 inverters each having theoutput thereof connected to the gate of a respective type NDS332P P-FET.The input of each of the inverters of the switch 112 receives the T2control signal 174. The two type NDS332P P-FETs are connected in seriesto form the two terminals of the switch 112, wherein a first terminal ofthe switch 112 is connected to the second terminal of the switch 104.The second terminal of the switch 112 is connected to the terminal 142to provide the output voltage V_(OUT1). The first terminal of the switch110 is connected to the second terminal of the switch 106. The secondterminal of the switch 110 is connected to the terminal 144 to providethe output voltage V_(OUT2).

The variable current source 122 of the embodiment of FIG. 16 comprisestwo type LM6152 OpAmps (U1B and U1A), two type NDS332P P-FETs (Q1 andQ3), a type 74ACT11240 inverter, and a type 2N3904 transistor (Q2). Theoutput of a first OpAmp (U1B) is connected to the base of the transistor(Q2). The variable current source 122 also comprises a 20 nF capacitor(C1) connected between the output and the inverting input of the firstOpAmp (U1B) and between the base and emitter of the transistor (Q2). A400 Ω resistor (R2) is connected between the emitter of the transistor(Q2) and the circuit ground 130.

The input of the inverter receives the T1 control signal 172, and theoutput of the inverter is connected to the gate of a first type NDS332PP-FET (Q1). The inverter and the first type NDS332P P-FET (Q1) interruptthe charge current to the charge storage component 114 when the chargestorage component 114 is discharging into the first load 146. The drainof the first type NDS332P P-FET (Q1) is connected to the collector ofthe transistor (Q2), and the source of the first type NDS332P P-FET (Q1)is connected to the non-inverting input of the second OpAmp (U1A). A200-ohm resistor (R1) is connected between the non-inverting input ofthe second OpAmp (U1A) and the input terminal 103. A 2-ohm resistor (R4)is connected between the input terminal 103 and the inverting input ofthe second OpAmp (U1A). The output of the second OpAmp (U1A) isconnected to the gate of the second type NDS332P P-FET (Q3). The sourceof the second type NDS332P P-FET (Q3) is connected to the invertinginput of the second OpAmp (U1A), and to the drain of the second typeNDS332P P-FET (Q3) is connected to the first terminal of the switch 104.A resistor (R3) 184 is connected between the input terminal 103 and thefirst terminal of the switch 106.

Note that in FIG. 16, the variable current source 122 is located in thepath between the input voltage terminal 103 and the switch 104 ratherthan being in the path between the switch 110 and the output terminal144, as described in FIGS. 4, 9, 12 and 13. It should be understand thatthe variable current source 122 in FIG. 16 is in the charging path ofthe charging component 114 and controls the charging current in the samemanner as described above in connection with FIGS. 4, 9, 12 and 13.

As discussed above, the regulating charge pump 1300 of FIG. 16 alsocomprises an error amplifier 124. The output of the amplifier 124 isconnected to inverting input of the first OpAmp (U1B) of the variablecurrent source 122 to regulate the current supplied by the variablecurrent source 122. In this embodiment, the amplifier 124 is a LM6152type operational amplifier (OpAmp). The inverting input of the amplifier124 is connected to the output terminal of one of the white LEDs 150.This enables the regulating charge pump 1300 of this embodiment to trackchanges in the forward voltage of the white LED 150. A voltage reference126 is connected to the non-inverting input of the amplifier 124. Inthis embodiment, the voltage reference 126 provides a fixed, 300 mVsignal. In alternative embodiments, the voltage reference 126 provides avariable signal. In further alternatives, the voltage reference 126 isselectable among a plurality of fixed values.

In the embodiment of FIG. 16, the output voltage V_(OUT1) on theterminal 142 is regulated at approximately 3.9 volts, which correspondsto a voltage at the output terminal of one of the white LEDs 150 of 300mV with a 3.6-volt forward voltage drop. The output voltage V_(OUT1) onthe terminal 142 is provided to the first load 146. In the embodiment ofFIG. 16, the first load 146 comprises a capacitive component ofapproximately 10 μF in parallel with a plurality of white LEDs 150.

The regulating charge pump 1300 also provides a second output voltageV_(OUT2) on the terminal 144 to the second load 152. In this embodiment,the output voltage V_(OUT2) on the terminal 144 is regulated to provideapproximately 40 mA of current to the second load 152. In thisembodiment, the output voltage V_(OUT2) on the terminal 144 is thevoltage present at the second terminal of the switch 110, and the secondload 152 comprises a plurality of green LEDs 154 connected in parallelbetween the V_(OUT2) terminal 144 and the circuit ground 130.

In the embodiment of FIG. 16, the second load 152 is interposed betweenthe variable current source 122 and circuit ground 130. In thisembodiment, the regulated current 156 flowing from the variable currentsource 122 is available to the second load 152 at the difference betweenthe voltage developed by the power source 102 and the steady statecharge on the charge storage component 114 minus losses in the switches104, 110.

The regulating charge pump 1300 of this embodiment also comprises a loadcurrent regulator 163. The load current regulator 163 regulates theISINK1 current 190 through a first white LED 150 of the first load 146and the ISINK2 current 192 through the second white LED 150 of the firstload 146. In this embodiment, the ISINK1 current 190 and the ISINK2current 192 are regulated at 30 mA each to provide improved parity oflighting from the two white LEDs 150.

The load current regulator 163 of this embodiment comprises a typeLM6152 OpAmp 194, two type FDV303N N-FETs 196, 200, two 5-ohm resistors202, 204, and a voltage reference (V_(RF2)) 206. In this embodiment, theV_(REF2) voltage reference 206 provides a fixed 150 mV signal to theinverting input of the OpAmp 194. The non-inverting input of the OpAmp194 is connected to a first terminal of the resistor (R10) 202, and theoutput of the OpAmp 194 is connected to the gates of the N-FETs 196,200. Respective first terminals of the resistors 202 and 204 areconnected to the sources of the N-FETs 196, 200, respectively. Thesecond terminals of the resistors 202, 204 are connected to the circuitground 130. The N-FETs 196, 200 operate as a current mirror so that theISINK2 current tracks the ISINK1 current, which controls the OpAmp 194.In the embodiment of FIG. 16, the voltage reference (V_(REF)) 126 in theerror amplifier 124 is selected to provide a sufficient voltage acrossthe N-FET 196 and the resistor 202 to ensure linear operation.

When the ISINK1 current 190 and the ISINK2 current 192 have magnitudesof 30 mA, the voltage appearing at the non-inverting input of the OpAmp194 of the load current regulator 163 will be approximately 150 mV, andthe voltage appearing at the drain of the N-FET 196 will beapproximately 300 mV. Thus, the error amplifier 124 will generate aminimal corrective signal to the variable current source.

In particularly preferred embodiments, the regulating charge pumps 100,200, 900, 1300 are fabricated on respective single semiconductor chipsin a manner well understood by one of skill in the art. However, it willalso be appreciated that the regulating charge pump 100, 200, 900, 1300described herein can also be fabricated from discrete components andwith circuit elements of different parameters to provide differentoperating parameters and to accommodate loads 152, 400 and powersupplies 102 having different parameters. It will be further appreciatedthat additional switches and charge storage components can be includedwith modifications to the switch timing control to enable alternativeboost multiplications in alternative embodiments of the invention.

Although the foregoing description of the preferred embodiment of thepresent invention has shown, described, and pointed out the fundamentalnovel features of the invention, it will be understood that variousomissions, substitutions, and changes in the form of the detail of theapparatus as illustrated as well as the uses thereof, may be made bythose skilled in the art without departing from the spirit of thepresent invention. Consequently, the scope of the present inventionshould not be limited to the foregoing discussions, but should bedefined by the appended claims.

What is claimed is:
 1. A multiple output regulating charge pump thatreceives a supply voltage and that provides at least a first output anda second output, wherein the first output has a first voltage and thesecond output has a second voltage, a current provided to a first loadconnected to the first output is actively current regulated, the firstoutput drives a first set of light emitting diodes, the second outputdrives a second set of light emitting diodes, and the first outputvoltage varies to compensate for temperature variations of the first setof light emitting diodes.
 2. A multiple output regulating charge pumpthat receives a supply voltage and that provides at least a first outputand a second output, wherein the first output has a first voltage andthe second output has a second voltage, wherein a current provided to afirst load connected to the first output is actively current regulated,wherein the first output drives a first set of light emitting diodeswhile the second output drives a second set of light emitting diodes,and wherein the first set of light emitting diodes are placed in aparallel configuration such that each light emitting diode conducts arespective current, and each respective current is controlled by arespective current sink.
 3. The charge pump of claim 2, wherein thecurrent sinks are current mirror circuits that each comprise at leastone transistor.
 4. The charge pump of claim 3, wherein a feedbackcircuit controls a charging current of the charge pump to ensure thatthe current mirror circuits operate linearly.
 5. The charge pump ofclaim 2, wherein the second set of light emitting diodes are placed in aparallel configuration and conduct a total current that is substantiallyidentical to a total current of the first set of light emitting diodes.6. A multiple output regulating charge pump that receives a supplyvoltage and that provides at least a first output and a second output,wherein the first output has a first voltage and the second output has asecond voltage, wherein a current provided to a first load connected tothe first output is actively current regulated, wherein the charge pumpcomprises a charge storage component and a plurality of switchesconnected to the charge storage component under control of a switchtiming control circuit, and wherein the switch timing control circuitcontrols the switches to connect the charge storage component in serieswith the supply voltage and the first output when the charge storagecomponent is discharged and to connect the charge storage component inseries with the supply voltage and the second output when the chargestorage component is charged.
 7. A regulating charge pump that receivesa supply voltage and that provides currents to at least a first load anda second load, the charge pump comprising: a charge storage component; avariable current source; a reference voltage; a feedback voltage; anerror amplifier that compares the reference voltage with the feedbackvoltage and that provides control signals to the variable currentsource; a plurality of switches that selectively interconnect thesupply, the charge storage component, the variable current source, theerror amplifier, the first load and the second load; a switch timingcontrol circuit that controls the switches such that the variablecurrent source supplies charging current to the charge storage componentand the second load; and a load current regulator coupled in series withthe first load, wherein currents within parallel branches of the firstload are actively balanced by current mirror circuits.
 8. The chargepump of claim 7, wherein the feedback voltage corresponds to a voltageof one of the current mirror circuits.
 9. The charge pump of claim 7,wherein the switch timing control circuit operates the switches suchthat the charge pump alternately provides current to the first load asthe charge storage component discharges and provides current to thesecond load as the charge storage component charges.
 10. The charge pumpof claim 9, wherein the first load is a set of parallel light emittingdiodes.
 11. The charge pump of claim 9, wherein the reference voltage isa fixed value.
 12. The charge pump of claim 9, wherein the referencevoltage is selectable among a plurality of reference voltage values.